Harvard Researchers Develop 3D Printed Synthetic Heart Valve that Grows with Children

A child’s heart valves can be damaged by rheumatic fever, which can then cause rheumatic heart disease and lead to even more serious health problems, such as stroke and heart failure. It is possible to repair heart valves through surgery, but it becomes much more difficult when you’re dealing with children whose bodies are still growing. Sometimes, several invasive surgeries are necessary to replace the valves with bigger ones, and it’s a costly, lengthy process to produce synthetic heart valves. But researchers from Harvard University are working to fix this problem with a 3D printed synthetic heart valve that’s designed to grow with a young patient—negating those extra surgeries.

A team at Harvard’s Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Sciences (SEAS), led by Kevin Kit Parker, PhD, is working to create this revolutionary pediatric heart valve. It’s called the FibraValve, and can be 3D printed in just ten minutes, out of a custom combination of polycaprolactone (PCL) and polylactic acid (PLA) called PLCL, using a new method called focused rotary jet spinning (FRJS). The technology allows the shape and properties of the valve to be customized down to the nanoscale level. As they explained in a recently published paper, the 3D printed valve was “readily colonized by living cells” in vitro and in large animal model studies, which were completed by collaborators at the Wyss Zurich Translational Center and led by Wyss Associate Faculty member Simon Hoerstrup, MD, PhD.

This representation of the FibraValve and FRJs appeared on the cover of Matter. Credit: Wyss Institute at Harvard University

“Unfortunately, current heart valve replacements do not grow alongside the child, necessitating repeat high-risk surgeries throughout the pediatric patient’s life. FibraValves are manufactured using biodegradable polymer fibers that allow for the patient’s cells to attach and remodel the implanted scaffold, eventually building a native valve that can grow and live with the child throughout their life,” the researchers wrote in their study.

Parker and Hoerstrup have been working to develop a living, growing heart valve for nearly a decade and produced their first synthetic heart valve, the JetValve, in 2017. This was manufactured using an earlier version of FRJS, where biocompatible synthetic polymer is extruded through a nozzle and spun into long nanofibers, which collect on a valve-shaped mandrel to quickly produce biocompatible valves. The pair successfully implanted their JetValve into a sheep’s heart, where it functioned properly and gathered living cells to regenerate new tissue, but they knew they could improve upon their initial design.

For the new FibraValve, the research team designed a valve-shaped frame, and using FRJS, added streams of air jets that filled the frame with liquid polymer. This enabled an easy adjustment to the final shape, and allowed them to improve the rate of fibers being deposited onto the mandrel. The result is a synthetic, 3D printed device with a mesh-like network of nanofibers that allows cells to infiltrate and grow.

Parker, the study’s senior author and a professor of bioengineering at Harvard, explained, “Cells operate at the nanometer scale, and 3D printing can’t reach down to that level, but focused rotary jet spinning can put nanometer-scale spatial cues in there so that when cells crawl up into that scaffold, they feel like they’re in a heart valve, not a synthetic scaffold.”

The FibraValve is composed of long filaments of polymer fibers, which replicate the physical properties of a human heart valve and are porous enough to allow cells to infiltrate and replace the scaffold with living tissue. Credit: Wyss Institute at Harvard University

Additionally, the team’s custom PLCL polymer material not only improves the infiltration of living cells once the FibraValve is inside the body, but is also biodegradable. A FibraValve is more elastic than its predecessor, and also allows for a more even distribution of cells throughout its scaffold. The team also optimized the shape of the valve’s inner “leaflets” in order to reduce how much blood leaked back through the valve. With all of these improvements, the FibraValve can actually remodel itself, which is why it is very useful for pediatric heart valve disease patients with hearts that are still growing. Plus, it only takes minutes to print one so it’s ready to be colonized by living cells.

“This study illustrates FibraValves’ potential as a solution for children suffering from valve diseases,” Parker said. “Our goal is for the patient’s native cells to use the device as a blueprint to regenerate their own living valve tissue, but FRJS also has potential as a platform to fabricate other medical devices in the future.”

A polymer and focused jets of air are forced through the spinning device, and fibers of the polymer collect on a valve-shaped mandrel to form the FibraValve. Credit: Wyss Institute at Harvard University

Hoerstrup’s team in Zurich implanted the 3D printed FibraValve into a living sheep’s heart, where it immediately began functioning, leaflets opening and closing to enable the regulated flow of blood with each heartbeat. An hour later, the researchers observed protein called fibrin being deposited on the outside of the valve, and red and white blood cells infiltrating its porous scaffolding, and saw no signs of side effects, thrombosis, or any other problems. Now, the team looks forward to evaluating the performance and regenerative capabilities of the FibraValve during longer-term animal testing.

Hoerstrup said, “From the clinical perspective, these first in-vivo results with FibraValve are promising and motivate us to initiate further pre-clinical evaluation.”

The researchers believe that their 3D printed approach to heart valve replacement could eventually lead to more customized implantable medical devices, such as blood vessels, other valves, and cardiac patches.